Compositions which contain polybutylene terephthalate and polyethylene terephthalate with fillers are described in U.S. Pat. No. 3,953,394. When compositions which contain polyethylene terephthalate resin and polybutylene terephthalate resin are melt blended with high levels of zinc oxide, a dense, ceramic-like molded article can be obtained. When compositions of either polyethylene terephthalate resin and zinc oxide or polybutylene terephthalate resin and zinc oxide are melt blended, the resin will exhibit a significant decrease in melt viscosity. The decrease in melt viscosity makes it very difficult to process the combination of the resin and zinc oxide, because the resin component is degraded. It has been found that compositions of polybutylene terephthalate, polyethylene terephthalate and zinc oxide may be prepared by melt blending without significantly depressing the melt viscosity of the resins. The melt viscosity is related to the molecular weight and the wet out of the filler. When the melt viscosity is not depressed by processing, the physical properties of molded articles will be improved as compared to test samples having a lower melt viscosity. This fact permits the use of melt blending to prepare compositions of polybutylene terephthalate, polyethylene terephthalate and zinc oxide which have good properties. It has also been found that very high levels of zinc oxide may be incorporated into a blend of polyethylene terephthalate and polybutylene terephthalate to form a highly dense composition having good surface properties.
The invention also provides a method of imparting stain resistance to a polybutylene terephthate-zinc oxide composition which is based on the addition of polyethylene terephthalate resin to said composition.
The highly loaded zinc oxide composition of the invention may be used for molding ceramic-like objects such as tableware, including dishes, bowls, mugs, and the like. It may also be used as a substitute for containers made of opaque glass or for molding billiard balls, poker chips and ceramic-like tiles. Containers made according to the invention can be used in contact with foods. The containers pass a standard FDA required test for metal extractables.
In addition, the addition of polyethylene terephthalate to a composition of polybutylene terephthalate and zinc oxide will improve the gloss of the surface.
Compositions of the invention have improved impact strength as compared to compositions that do not have a combination of polybutylene terephthalate and polyethylene terephthalate.
Accordingly, it is an object of the invention to provide a molding composition which contains high levels of zinc oxide which when molded will have a smooth and glossy surface.
It is also an object of the invention to provide novel molding compositions which have a ceramic-like feel and density.
It is also an object of the invention to provide novel molding compositions which have a special utility for molding molded articles such as tableware.
It is also an object of the invention to provide novel molding compositions which have a special utility for use as a substitute for opaque glass.
These and other objects will become apparent from the present specification.